This invention concerns improvements made to tamping rammers for tamping the ground, and mile particularly to the structure of a tamping plate of a tamping rammer.
A conventional tamping rammer shown in FIG. 6 comprises a tamping foot 32 comprising an inner spring cylinder 34 and an outer guide cylinder 33 which are inserted slidably to each other below a power transmission system 31 which changes rotational movements of an engine 30 to vertical movements, and a tamping plate 35 at the lower end of the tamping foot 32. As vertical movements of the transmission system 31 are transmitted to a coil spring 37 positioned inside the spring cylinder 34 via a piston rod 36, the vertical movements of the spring cylinder 34 generated by compression of the coil spring 37 are transmitted to the tamping plate 35. This structure is widely known, for instance, from Japanese UM Kokai Heil-84307.
The above mentioned rammer generally requires a coil spring 37 with a large spring constant in order to efficiently perform tamping of the ground C with a strong impact force by increasing the amount of jumping of the tamping plate 35.
In this type of rammer, the centerline A of the machine body along the longitudinal direction of the guide cylinder 33 and the spring cylinder 34 comprising the tamping foot 32 is tilted frontward in respect of the bottom face of the tamping plate 35 contacting the ground so that the machine automatically advances repeating jumps of the tamping plate 35. Generally, there is provided a sleigh-shaped component with the front end or the front and rear ends standing upright from the bottom face of the tamping plate 35 for securely supporting the machine body, and the entire bottom face contacting the ground is flat and parallel to the ground.
In some rammers, the bottom face of the tamping plate is shaped like a hill when looked from the side as disclosed in Japanese UM Kokai Sho62-196209, or has a spherical surface as disclosed in Japanese UM Kokai Sho58-165005.
On the other hand, a conventional rammer, of which tamping plate 35 has a flat ground-contacting face at the bottom which is entirely parallel to the ground as shown in FIG. 6, is used for tamping the soft ground or the relatively hard ground paved with asphalt depending on the purpose of work. In this case, increasing the amount of jumping of the tamping plate 35 by the coil spring 37 with a large spring constant as discussed above achieves effective tamping and presents no problems even if the ground is soft.
However, it the rammer provided with a coil spring having a large spring constant is used to tamp the relatively hard ground surface paved with asphalt, etc., impact resilience between the ground and the tamping plate 35 becomes high, making jumping behavior of the rammer unstable and causing it "to dance", creating problems for the operator.
The rammer on such an occasion jumps swaying lengthwise and crosswise, and the tamping plate cannot carry out strokes parallel to the ground.
The inventor of this invention studied causes for such unstable jumping behavior when a conventional rammer is used for tamping the hard ground, and found out that the tamping plate of a conventional rammer has a bottom face that is completely parallel to the ground except for a tilted surface standing upright at the front end of the plate.
As shown in FIG. 6, the centerline A of the tamping foot 32 of the rammer is tilted forward in respect of the ground-contacting face of the tamping plate 35 in order that the machine automatically advances while repeating jumps. Thus, the machine jumps in the direction along the centerline A.
On the other hand, the center of gravity G of the machine is positioned at the rear of the centerline A at the middle of the machine height so that the machine is stably supported instead of falling forward when the bottom face of the tamping plate 35 contacts the ground C. However, as the tamping foot 32 is tilted forward as mentioned above, the point E on the bottom face of the tamping plate 35 that receives the perpendicular line B from the center of gravity G is in the front of the point D on the bottom face of the tamping plate 35 where the centerline A passes.
As shown in FIG. 7, when the rammer jumps to a certain height and then falls, the tamping plate 35 hits the ground C and the center of gravity G moves forward by a large margin beyond the point D on the bottom face of the tamping plate 35 where the centerline A passes. The tamping foot 32 assumes a frontward tilting posture so that the angle .theta.2 between the centerline A and the ground C becomes larger than the angle .theta.1 shown in FIG. 6.
As the center of gravity G leans forward beyond the point D where the centerline A passes at the moment when the tamping plate 35 hits the ground C, the centerline A assumes the frontward tilting posture with the angle .theta.2. Since the bottom face of the tamping plate 35 is entirely flat, it momentarily becomes unstable with its rear end floating up and creating a void between the ground C and the point M, which is ahead of the point E supporting the center of gravity G.
When the machine jumps and the tamping plate 35 rises at the next moment, the machine is unstably supported at the point M, which is in front of the point E receiving the center of gravity G. As shown in FIG. 8, the machine then jumps bending backward (to the right) and the tilting angle .theta.3 of the centerline A becomes smaller than the original angle .theta.1 shown in FIG. 6, causing the tamping plate 35 to hit the ground from the point N at its rear end, thus creating unstable conditions again.
Movements mentioned above were described in respect of the lengthwise direction of the machine. In practice, such movements occur also in respect of crosswise direction because of a similar reason or because of the irregular ground surface. Thus, tamping the hard ground with a rammer creates extremely unstable jumping behavior of the machine, forcing the operator to work with extreme difficulty.
In order to prevent unstable jumping behavior of the machine when tamping the hard ground, the stroke length of the tamping plate may be shortened or the spring constant of the coil spring may be minimized. However, such measures are not enough to achieve sufficient and effective tamping effects even though the work may be performed perfunctorily.